1. Field of the Invention
The present invention relates to a method for producing silicone rubber moldings. More particularly, this invention relates to a method for producing silicone rubber moldings having a smooth, hard exterior layer and a relatively soft interior portion without the necessity of appling a coating to a finished, cured molding.
2. Description of the Prior Art
Unitary silicone moldings composed of a hard exterior layer and a relatively soft interior portion are used as buffering elements and protective coating elements. With regard to methods for producing such moldings. Japanese Patent Publication Number 59-30932 [30,932/84] discloses a method in which a porous element, for example, a sponge or a cloth is impregnated with a room temperature-curable silicone rubber to afford an uncured or semi-cured gel-form molding. This molding is then immersed in a curing agent for the silicone rubber and the molding's exterior layer is completely cured. U.S. Pat. No. 4,517,238. which issued to Mine et al. on May 14, 1985 teaches forming a molded product by applying an addition reaction curable organosiloxane composition to the surface of a substrate and then applying only the organohydrogensiloxane reactant of said composition as a coating. The coating forms a highly crosslinked layer on the surface following curing of the composition.
The disadvantage of the aforementioned prior art methods is their inability to produce moldings with good dimensional accuracy and a uniform, hard coating on the surface of the cured article. Furthermore, the methods used to produce these prior art cured articles are complex, requiring a step during which the organohydrogensiloxane is applied as a coating to the molded article followed by a second step during which all of the materials are cured. The maximum rate at which cured articles can be produced is therefore relatively low.
The present inventors conducted a vigorous investigation with a view to eliminating the aforementioned problems, and the present invention was developed as a result.